Ground speed indicator



6 Sheets-Sheet 1 Filed April 5, 1949 III: lllll. llllllllnlllllll Feb.5, 1952 A. G. THOMAS GROUND SPEED INDICATOR 6 Sheets-Sheet 2 Filed April5 1949 INVENTOR Feb. 5, 1952 H 2,584,641-

GROUND SPEED INDICATOR Filed April 5, 1949 6 Sheets-Sheet 3 35 646-1] 1V s i i u VINVENTOR A. G. THQMAS GROUND SPEED INDICATOR Feb. 5, 1952Filed April 5, 1949 6 Sheets-Sheet 4 Dl-sm F7? 6 why 1,35

Til 203 @202 3% INVENTOR.

Feb. 5, 1952 Filed April 5, 1949 6 Sheets-Sheet 5 ,r I g 42 23 i 238$ zwa /WW Feb. 5, 1952 VA. G. THOMAS 2,584,641 7 GROUND SPEED iNDICATORFiled April 5, 1949 6 Sheets-Sheet 6 IN V EN TOR.

Patented Feb. 5, 1952 UNITED v STATES PATENT oFFlc f? 7 Albert G.Thomas, Lynchburg, Va.

Application April 5, 1949, Serial No. 85,581

14 Claims.

This invention relates to instruments generally and particularly toground speed indicators for aircraft.

It has long been a problem to provide a. ground speed indicator forairplanes and other aircraft, and. which will be accurate, simple tooperate, and not requiring the operator to see the ground, which termalso includes bodies of Water such as the sea. It has also been aproblem to provide aircraft with a reliable gyroscopic compass sinceknown gyroscopic compasses tend to veer from true indications in arelatively short time.

An object is, therefore, to provide an instrument for aircraft or othervehicles for indicating true speed of the aircraft relative to ground,even though the ground is not visible.

Another object is to provide an instrument for aircraft or othervehicles for indicating'true direction of flight or travel.

An additional object is to provide a ground speed indicator which alsoshows drift.

Additional objects will be evident in the following description.

In the drawings:

Figure 1 is a top'plan view, in part section, of

"a ground speed indicator employing two gyroscopes and a pendulum orplumb bob. The gyroscopes are indicated by dotted circles and a baseplate is shown broken away.

Figure 2 is a right side elevation, in part section, of the device shownin Figure 1.

Figure 3 is a fragmentary elevation, in part section, of a gyroscope andplumb bob mounting suitable for use in the device of Figures 1 and 2.

Figure 4 is a fragmentary elevation of another plumb bob mountingsuitable for use with the device shown in Figures 1 and 2.

Figure 5 is a front elevation,'with parts broken away, of a balancedplumb bob mounting associated with a universal gyroscope mounting.

Figure 6 is an elevation of a spherical split shell holding a motor andgyroscope, showing associated rods broken away.

Figure 7 is a sectional view of a shell similar to that shown in Figure6, showing the split threaded construction.

Figure 8 is a fragmentary top plan view, in part section of a modifiedcam construction, and showing associated elements.

Figure!) is a side elevation showing a modified bearing for the outerbearing ring of Figs. 1 and 2, andindicating the inclination of plate Iand several associated elements for flight at a latitude other than theequator.

the construction and setting of cams-or wedges as shown in Fig. 1, fornorthward flight.

Figure 11 is a fragmentary top planview showing the setting of thewedges of Fig. 10, for southwardflight.

Figure 12 is a fragmentary top plan viewshowing a modified constructionfor the lower ends of plumb bob and gyroscope rods, and associatedstops.

Figure 13 is a fragmentary rear elevation showing the stops of Figure 12and supporting plate.

Figure 14 is a top plan view, in part section, of an electrical groundspeed indicator, showingta casing with cover removed.

Figure 15 is a top plan view of a modified electrical ground speedindicator. I

Figure 16 is a right face view of a contact disc used in the deviceshown in Figure 15.

Figure 17 is a "diagrammatic sketch of another modification of theelectrical ground speed indicator.

Figure 18 is a schematic illustration of still another modifiedelectrical ground speed-indicator. 1

In Figures'l and 2 plate I is mounted centrally in circular ring 2 whichis rotatable in outer bearing ring 3 which is rotatable about ahorizontal axis including bolts 4 fitted into holes in verticalsupporting legs 5 integral with horizontal upper base plate 6 whichrests upon lower base plate and can be rotated relative thereto aroundpivot 8 which passes through a central hole in plate 5 and is screwedinto a threaded hole in plate I. Bolts or pivot pins 4 have threadedportions 9 screwed into threaded openings in .ring 3 and cylindricalbolt tips ID are fitted into circum-- ferential groove l l around ring2,.to allow relative rotation of the rings but not relative axialdisplacement. Suitable washers are provided between posts 5 and ring 3so that the lattencan be rotated about pivots 4 through an-anglerelative to posts or legs 5. r

Slide or carriage I 2 is slidable along track. or trapezoidal key 13which is fastened to plate I and extends across the inner diameter ofring 2 as shown. The portions Ic of plate I are made of slightly lesswidth than the rings. A trapezoidal slot is provided in the lower partof slide l2 and is fitted over key [3. Cams l4 and I5 are, attached toslide l2 by means of adjustable slides and project upward therefrom. Theconstruction is described in detail in connection with. Figs. 10

and 11. a Rectangular rod I6 is attached to inner spheri- Figure 10 is afragmentary top plan. iew ch cal gyroscope shell l1 (Fig. 2) which isrotatable in any direction through limited angles within outer sphericalsupporting shell l8 which is fastened to arm l9 integral with postfastened to plate I. Gyroscope 2| is mounted for rotation within innershell I1 and may be driven by a separate motor as shown in Figure 6 orit may comprise a combination motor and flywheel or gyroscope asillustrated by gyroscope-motor 22 (Fig. 2). Such...combination motorsand gyroscopes are known. lEShell i8 is splitalong 'plane 23 and thehalf shells can be threaded together or fastened together with screws orin any suitable manner. Shell I8 is provided with top and bottomcircular openings 24 and 25f-WhlCh-"2I11OW limited movement of rods 26and L6. attached to inner shell I! diametrically opposite. Rod'25 isshown broken away but may be as ilongaas rod Hi. In any event it servesto balance the latter .rod so that shell I! will remain in any positionin which it is placed relative to shell l8. Inner 'shell' l1= may=alsobe split so 'that-the'contained gyroscopeemotor -can be inserted andremoved 7, vi'zh'en *"c lesi-r'd. The construction may "be as showninFigure 7' or '-the"halves can be fastened by screws, suitable bearingsbeing provid'ed with- 'in' 'the shell for-the gyrescope which is alsobalanced. V

Gyroscope=mdtor 22 is "mounted on shaft *2! which is rotatable inbearings 28 and 29?:fastened -totire -interior 6f spherical shell 30which V issuitablysplit. -"Shell 30 "istra'ther thickarid-hascircumferential 1 groove 3l-as shown in Figure '7. Th'e shell is s'h'ownas compr'ising' two parts, one screwed into the other b'y meansofthrea'ded shoulder '32 arid cooperating threads on the 010- positehalf-shell. Before screwing :the shell "'halves to'gether, ring 33 Figs;2 and 6)- is placed on shoulder 34, -"for instanca so that the ringwillbe' h'eld in lateral po's'ition"in grooveiSl when the-shell 30isassembled. Ring '33 isfreely rotatable in groove 3| around assembledshell 30, unless purposely locke'd thereto. This ring carries-depending;attached, rectangular rod 35 andplaced diametrically oppositebalancingrod "i'fipshown 'broken away. Rod "36 is arranged to balance"rod 35 so t-hat? the 'latter' will ordinarily "remain -in any position'in which it "is placed, rela- 'tiveto outer supporting orbearingaspherical jshell "31 which"is"-fastened to theend of arm "i9.insany "suitable-"manner. "-R;ing '33"is 'slig'htlyi-less thick thanthedepth of'-'gro"ove"'3l so' that"it:will not "rub against-thednnersurface "of'" shell 31. This "shelhhas oppositely positioned slots 381andr39 which extend somewhat-more than :9 0. degrees 3 so "'that'rods36 and35 can berotatedito a position parallel with'plate "I. Theseslotsare :considerably 'wider' than 1 ods 3 5 and-3 6 so that the :latter canbe moves-m any direc'tion-within limited angles.

"The" motor of *gyro -'motor "22 can -'beasuppl-iecl 'ele'ctric' currentthrou'gh slip "rings '49 on: shaft"! 1, extended, and suitablecooperaitingbrushes are fprovi'ded. "Flexible "electrical conne'ctionslike ;coi1ed wires 41 of FigureS can beused to-bring Jcurrent tothe'=brushes and atthe same time to allow"practic'ally unhinderedrelative movement fbetween 'sh'ell 3'0 and outer shell srwmcmsnawclosely toshellifl but allows free movement of thelatter. Ball bearings'can"be 'place'd'in recesses, between the shells, if desired. Wires 4 lare' brought out.of shell'30through holes therein. As shown in'Figure 6,shell'30 is assembled, with. rotatable ring 33 in.groove 3| .andcarrying rods 35 and -3=B shown. in l'fragmentary' manner. "In this casea separator mot'o1"'42isshownat- 4 1 tached to the inner surface ofshell 30 and motor shaft 2'! carries gyroscope Wheel 22a. The motor,gyroscope wheel, and other parts within shell 30 are so balanced thatshell 30 will remain in any position within shell 31, in which it isplaced. This is to eliminate undesirable torques on the gyroscopetending .to make it precess. Gyromotor 22 is similarly balanced as Wellas gyromotor 2|. The separate motor and gyroscope wheel of Figure firepresents anzalternative construction. There should be as littlefriction as :possible between shells 30 and 31 as well as between shellsl1 and I8.

"-iThefgeneral principles underlying this ground speedand driftindicator are, thatthe rate of ap- 'parent' rotation of a gyroscoperelative to its supzportpdue toirotation of the earth, is changed inproportion to the speed of the supporting vehicle "irran'east-west orreverse direction; and that the degree of divergence within a givenperiod of time of aplumb' line from anlinitial' startin'g position in registerrwith a gyroscopically z'controlled indicator is a measure of thespeed ofthe'z-aircraft :or:other supporting 'vehicle-in amorthesouthdirection; or the reverse. vThe axis :of :the': first namedgyroscope-should :lie inza :planezparallel with the equatorial plane :of:the :earthxandt the axis of the other or north-south iigyroscopeshouldbe kept parallel withIthegaxis: of. theearth,

during the 'periodof the test. ;The resultantzof thesetwo speedindications will,;shoW1the-.:true ground, speed of the;aircraftror1other vehicle and the course or trueidirectionzofatravel:iwillsalso beindicated. The adriftcan be :read; as azcomponent of the speed.

The gyroscope used torindicatexthe castawest component of speed-willmake one :lapparent revolution every 24rhoursawhether'thersupportzisattached to the earth or.to;an-.aircraft:since-the atmosphere is sweptalongfwith theeartheatcomparable speed. If.desiredjhiss gyroscope cam-berotated. byclockwise prjthe :like at .;a:;ra'.te ;of;.one revolutionevery 24 hours and the gzincreased'or reduced displacement of thegyroscope indicator, aftera predetermined intervalzoftimeavillibe ameasure of {the westeto-east grounds-speed, or

east-to-west ground -;speed, :respectively. The reason for this :is':that the apparent rotation, of

that it can movebetween the=closely-adjacent ends of we'dgesor cams l4and ii 52in a-direction along, say, the X axis or perpendicular'to'the'long or Y axis of slide I2.

The :initial position of rod I6 for any speed determination is indicatedin Figs. 10 and 11.

Assuming that *the aircraft -is' flying northeastward, arrow EW ispointeddue'eastand the timing mechanism to' be described' later isreleased. Then there is an apparentdisplacement of rod [6 in thesame'd-irection as'indicated by'arrow E-W'and parallel to it."The-dimensionsytiming, and other factorsiare'soichosen that thisdisplacement, due to rotation 'of'the earth and its'atmosphere andconsidering the aircraft as stationary, will bring the rear face 16a tothe right until it is inregister withthe right edge of end I4a.Therefore, at this point,

yond the right edge of end I4a within the predetermined time intervaland the greater will be the possible movement of slide I2 before it isstopped by the flared cam I4 striking face Ifia or, its edge. Thereforethe displacement of slide I2 relative to scale OE on plate I and alignedparallel with the slide, is a measure of the eastward component of theground speed of the aircraft, assuming flight near the equator.Actually, rod I6 is maintained in its alignment in space by attachedgyroscope 2|, and slide I2 and attached cam I4 are moved relative to it,due to flight of the aircraft in a circular are above the earth but rodI6 appears to move relatively. The cam or wedge construction provides arelatively simple means of obtaining large proportional movements of onemember with respect to small movements of a cooperating member. Gears,levers, electrical amplifying systems, or other means can be usedhowever.

At any latitude the angle of plate I, relative to the horizontal, isadjusted so that relative apparent movement of rod IE will be in a planeparallel with the equatorial plane of the earth. If rod I6 is longenoughthe arcuate relative displacement of its end can be considered asstraight line displacement, for small arcs, which will usually be thecase. If extreme accuracy is desired, however, the flared surface of camI4, the surface I611, or both, can be so curved or shaped that lineardisplacements of cam I4 will be directly proportional to relativeangular displacements of rod I6. Cam I may be similarly shaped.

Similarly, the end of rod 35, and cam 8'! can be .curved to compensatefor arcuate movement.

An aircraft flying at a rate of several hundred miles per hour will in afew minutes cover an arc 'of or more, so that the displacements of thean oblate spheroid to conform to the shape of the earth, if desired.

Elongated slot or groove 49 is cut in plate I parallel with the longaxis of slide I2 and slightly spaced therefrom. Elongated rectangularslide 50 is slidable in slot 49 which should be of sufficient depth tohold slide 50 upright, although any suitable guides or supports may beused.

:The bottom of groove 49 can have a long, narrow central slot throughwhich guide bolts can be screwed into threaded openings in the bottomedge of slide Bil. Thin rectangular plate 5! is vertically slidable in asuitable slot in slide 50 and is urged. vertically upward againstrounded element; by means of suitable springs placed in the slot.Therefore, rotation of .cylinder will, through friction, move plate 44and slide I! through a corresponding distance along track I3 thedirection of movement depending upon the direction of rotation of thecylinder. At the same time the rotating element 46 will, throughfriction, cause movement of plate 5! and slide 50 along slot 49, thedirection of movement being the same as that of slide I2 and parallelthereto. ihe amount of displacement of slide 50 will however be lessthan that of slide I2, for the position of element 46 illustrated sincethe effective actuating diameter is less than that of cylinder 45. Whenthe aircraft is flying near the equator shaft 41 is shifted until theupper edge of plate 5I is in contact with the full diameter of cylinder45, and when flying at other latitudes, shaft 41 is shifted so that thediameter of element 46 in contact with plate 5| is reduced in the sameproportion that the circumference of the earth at the latitude of flightbears to the earths equatorial circumference.

While frictional drives are shown for the plates 44 and 5! it is obviousthat the upper edges of these plates can be provided with rack teeth andsuitable circumferential teeth cooperating therewith can be provided oncylinder 45 and element 46. In case the friction drive is used thesurfaces may be roughened or magnetized to produce better traction.

Shaft 41 carries thin rigidly attached disc 52 which can be rotated inslot 53 in arm 54 which can be shifted to the right or left by integralarm 55 at right angles thereto and of rectangular cross section. Arm 55is slidable to right or left in a rectangular slot in bearing guide 56attached to an edge of ring 3 as indicated. Thin striplike cam 5'! isattached to an edge of ring 2, and extends slightly more than half wayaround this ring, as shown particularly in Figure 2. The cam startsrising at point A and continues to rise until it reaches point Bapproximately and then declines continuously until point C is reached.Point B is 'an index to show the setting of cam 5'! and ring 2 withrespect to surrounding ring 3 which carries arcuate scales Se and $1.0marked off in degrees of latitude on either side of the zero point ofthe scale which is shown as being in register with index B of the cam.This setting is used for flight at the equator. When however a groundspeed determination is made at any other latitude, index B is turneduntil it is in register with the indicated latitude on scale Se or scaleSw, depending upon the general direction of flight, as described later.For flight south of the equator the scales would be used in oppositeorder.

The reason for making the above described adjustments is to have theplane of plate I parallel with the axis of the earth, during a groundspeed determination. In this way rod or arm I6 is caused to precess in aplane parallel with the equatorial plane of the earth, for any latitudeat which the aircraft may be travelling. Furthermore, this adjustment ofring 2 and attached plate I causes the axis of gyroscope 22 to beparallel with the earths axis when the plate is oriented with respect toattached magnetic compass 58 so that arrow E-W lies in a true east-westdirection.

Scales Se and Sw and the two rises of cam 51 are calibrated and relatedto the diameter or curvature of element 46 so that any setting of indexB on ring ,2, with respect to latitude scale Seer S10 will cause element46 to. :be shifted to the right-or left until it is properly set to moveplate 1- and slide 5%) a proper distance to compensate for latitude, fora predetermined angular rotation of shaft 51,. Tension spring 59 isattached to guide it and to arm 5.4 to hold the end of arm '55yieldingly against cam 51. The angular position of this camthereforedetermines the lateral position of arm 54, disc 52 and therefore element46.

The right end of the shaft t! is slidable in axialiy bored cylinder [itwhich is connected with the adjacent face of disc 52 by means of torsionspring 8! surrounding the shaft. The right face or end 10f -'cylin deris rigidly attached to short shaft 32 having rotary bearing in posts 63and G l; extending upward from plate Shaft 62 is coaxial with shaft lland is prevented from axial movement, by attached gears 65 and 66 oneither-side of post 64*. Spring (it allows shaft 62 and attachedcylinder 69 to be rotated through a considerable angle without rotatingshaft 41 which may at times be held by the friction between plates 3 and5t and cylinder 45 and ele ment' 26. tangular slot in block 59, parallelto plate l, is placed beneath gear (it, in mesh therewith. Block 69isxatta'ched to plate i and has another rectangular slot guidingmovement of rack 88 parallel with rack 5i. ear 65 with rack teeth in thelower surface of the rack and aligned to rotate gear 65 in a (iirectionopposite to that produced by rack er acting upon gear 65. Both racks t7and t6 are normally held out of contact with the respective gears bymeans of compression springs 19 and 'I i yieldingly urging the buttons12 and E3, and attached rack bars 81- and 68, respectively, outward fromblock til against which the springs press. The rack bars' are limited inoutward movement by respective pins 14 and 15, project ing. from theirupper surfaces, striking block 69. Button 12' is pressed toward block 69to register a ground speed indication for westward flight and button '13is pressed toward block 59' to register a ground speed indication foreastward flight. Since only one button is pressed at a time the racksdonot interfere with each other andshaft 4? can be rotated in eitherdirection.

Arm I6 is attached to the upper end of sleeve 7! through which pivotscrew '38 passes and is screwed into a threaded opening in plate i. RackS'l'is situated lower than rack 68 and so pin 14 is'longer than pinliiso that either pin will strike armlfi to rotate the arm and sleeve 18about the pivot when the corresponding rack is pushed its full traveltoward or past shaft 62. The buttons and springs 1!! and ii limit therack movement. Arm i'9'is attachedto sleeve T'l'below arm 16 andcarries-attached arcuate cam 81' beneath it. This cam is-concentric withpivot i8 and, in use serves to'force arm 8i, pivoted at 8-2 to plate I,around pivot 82 so that V notch 83 in the arm will be forced againstpeaked rod 84 to align this rod. Rod t4 passes through attached plumbbob- 85 and only the lower end of the rod needbe peaked. This rodextends further toward plateil than rod 35 which depends from gyroscopeshell ring 33. (See Figure 2.) The reason for this is that the adjacentfiat face of' rod 84 will strike slide 86 as a stop and the lower end ofrod 35 will then serve: to stop movement :of cam 81 fastened toslideaBGabove it, in the same way that rod [.6 servesto stop movement ofcam [4 or cam I5.

0am rise 88'Jis attached to plate 1 near slide Rack 61 which is guidedby a rec- Rack 38 is placed above 8. 86 andis struck by the V end of arm8| to force that arm to rise when moved toward arm 84 so that the lowerpeaked portion of that arm will be gripped by the V slot and will beproperly aligned when a ground speed determination is desired. Whenbutton 12, which is shown pressed toward block 69, is released, tensionspring 89 attached to arm 16- and pin-90 on block 69, pulls arm 16counterclockwise about pivot 18 (Fig. 1) and arm 15! and cam strip 80are similarly rotated until the cam is not in contact with arm 8i. Thentension spring 9-! attached to arm 81 and to plate I pulls that arm awayfrom rod 84 and downward ofi cam '88 and against stop 92 so that arm 8!will not then obstruct movement of arm 84 away from slide 36. Pivot pin.82 is vertically movable in a hole in plate I, to allow the lifting andlowering of arm 8!. Arm 16 is normally held against pin 15 which isforced against block 59. The movement of either rack will cause circularmovement of arcuate cam 80 sufficiently to wedge the V arm 8| againstrod 35. Any excess movement of the cam does not cause further pressureon arm 8| since the cam is concentric with pivot 18. 'Ihe cam isarranged so that it does not strike post 63 or post 64 when spring 89causes its return-to starting position. It is shown in the positioncausing pressure of arm Bl against rod B l.

Tension spring 93 is attached to the end of arm 19 and to cable Sl iapassing around pulley 93d and connected to pin 94 extending from slide86. Pulley 93a is rotatably fastened to plate I by screw 9%. Slide 86 ismovable in elongated groove or slot 95 out in plate i and aligned atright angles to the long axis of slide [2. Groove 95 should be deepenough to guide slide 86 properly but additional guiding means can beused as described in connection with slide [2. The faces of slide 86 areperpendicular to plate I. Tension spring 96 in slot 95 is attached tothe end of the slot and to slide 85 and normally keeps the slide pulledto its extreme right position with the left end of cam 8'! at rod 35 orbeyond it. When, however, arm 19 is swung around pivot 18 in clockwisedirection as illustrated, the slide is pulled to the left, unlessstopped by rod 35, by cable 94a and spring 93 which is sufiicientlystiff to overcome spring 96 but which allows arm 19 to make its fulltravel as determined by the movement of pin 14 or pin 15. When eitherpin is moved through its full travel toward shaft 62 by its associatedrack bar, arm 19 is rotated sufficiently to cause spring 93 to pullslide Bite the left for practically the full length of cam or wedge 8'!if the lower end of rod 35 does not obstruct the displacement. If,however, rod 35 is displaced relative to rod84 and toward cam 8'! asuflicient distance, then'the cam will strike rod 35 and will be.limited in movement thereby. Rod 35 is locked in relative position bypin 5'20 (Fig. 3) before spring 93 is pulled by arm 19. Upon release ofbutton 12 or button 13, spring 96 pulls slide 86 back to the right toits starting position.

Right angle arm at is attached to a face of wedge 81 near its leftendfland carries attached thin tube 99 the axis of which is vertical tothe plane of plate i. This tube has lower end flange 196 which isslidable in a guide slot starting at the left end of rectangular .barl0! and continuing nearly its full length. The upper face of the bar iscut away to form open slot H12 of less width than the connected guideslot for the flange. Tube 99 projects upward throughslot it? and hascross hairs I03 in register with scale I04 extendin'g centrally alongthe bottom surface of the guide slot and calibrated, preferably, inmilesper-hour ground speed. The zero point of this scale is at the axisof pivot pin or screw I which passes through a hole inbar It! and isscrewed into a threaded hole in slide '50 near its end, as indicated.Bar Hll may be made'of transparent plastic or other material, ifdesired. The cross hairs I03 can then be read. with respect to scale I04and also with reference to scale O-NS marked on plate I and alignedperpendicular to scales OE and OW. Scale O-NS is preferably calibratedin miles-per-hour ground speed, as are scales OE and OW. Scale ONSserves to indicate the true north or true south component of groundspeed of the aircraft. The zero point of this scale coincides with theaxis of screw I05 when scale I84 lies above scale O-NS in alignmenttherewith. The east or west component of ground speed can be read onscale OE or OW, respectively, by projecting a line from the axis ofscrew or pivot I85 to scale OE or scale OW, at right angles thereto Anindex on slide 50 can indicate the position of this axis with respect tothe above scales.

It is apparent, therefore, that if zero point 185 is shifted along scaleOW as indicated, and if the cross hairs 13 are shifted along scale ONSby arm 98 toa point representing the true north or true south groundspeed-component, then the true or resultant ground speed of the aircraftcan be read on scale I94 as the distance from zero point I05 to theintersection of scale I04 with the cross hairs. The bar HlLwill slippast tube 99 as a pivot, as screw I 05 and slide 50 are moved to oneside or the other, parallel with scales OE and OW. When slide 86 isresting in displaced position against stop 91, cross hairs I03 aredirectly over the axis of pivot I05, at zero position.

The component speeds as indicated on the scales are measures of drift asdetermined for any desired direction since the apparent direction offlight as indicated by the fore-and-aft axis of the aircraft can becorrelated to the component speed at right angles to the apparentcourse, or along any other line desired, including the scale axesthemselves. If drift in east or west direction, or in north or southdirection is desired it can be read directly from the scales. If drift,considered as a perpendicular rate of displacement from the apparentline of flight is desired then the drift will be measured in terms ofthe sine of the angle between the apparent course and the actual courseof flight.

The actual flight path is indicated in degree by the angle that scaleI04 makes with respect to scales OEO-W or with respect to scale O-N Theangle may be measured by a movable pro-- tractor which can be a part ofthe instrument.

The scales OE and OW are marked for flight north by east, and north bywest, respectively. In case the aircraft is flying in generallysouthward direction, in one mode of operation legs 5 can be rotated 180aro-und pivot8, or the whole device can .be shifted so that arrow E-Wpoints due east as for northward flight. By this procedure gyroscope rod[6 will still have the same relative movement withrespect to cams orwedges I4 and I5 as before and east-west speed components can be read aspreviously described. The relations betweenplumb-bob controlled rod 84andgyroscopically controlled rod 35 will, however, be difierent in thiscase than for northward flight, since the plumb bob rod'tends to legbehind 10 the gyroscope rod due to travel northward or southward aroundthe earth. The gyroscope rod tends to maintain its alignment in spaceand the plumb bob rod tends to point toward the center of gravity of theearth. Since if the device is rotated after turning the aircraft 180 tofly south, arrows E-W and NS will be in the same directions relative tothe earth for southward flight as for northward flight and the rod 84will tend to lag behind rod 35 in opposite sense to that described.

Means for utilizing displacement of rod 84 in either direction relativeto rod 35 are shown in fragmentary Figs. 12 and 13. The rods haveinclined surfaces meeting on a relatively narrow line 8811 so that thesame displacement of either rod, toward cam 81 will stop the camvirtually in the same position as it moves to the left. The locked rodsare aligned as before by the V slot and peak and are forced by arm 8|,slightly resilient in this case, until rod35 strikes stop 202 forsouthward flight and until rod 84 strikes stop 203 for northward flight,since in the first case rod 84' projects beyond rod 202 and stopsmovement of cam 81 and in the second case, rod 35 projects beyond rod 84and stops cam 81. Stops 202 and 203 are two stiff metal strips either ofwhich can be vertically moved through its guide slot in plate I, upwardto serve as'a stop or downward to be moved from the path of theassociated rod, being held in position by friction. Stop 202 is pulledup for southward flight and stop 203 is pulled up for northward flight.

In addition to the displacement between the two rods due to the flightcom onent along a meridian, there will be a certain side shift betweenthe rods due to the earth's rotation and to flight in paths other thantrue north or south. This component at right angles is not used in thetests however since V arm 83 aligns rod 84 sidewise, and rod 35 lockedto it, for any test.

As shown in Figure 8, cam 81 can be inclined or curved on both faces, sothat it can be used for either direction of travel, northward orsouthward. In that case pendulum rod 84 should be free to swing oneither side of slide 86 since the rod 84, pointing toward the center ofthe earth, will be at an angle to the plane of plate I except for flightat the equator where it will be perpendicular. For northward flight therod will swing toward edge la of plate I but if the plate is turnedthrough 180 for southward flight, then pendulum arm 84 will swing towardedge lb, and cam 81 or slide 86 should not obstruct this movement instarting position. The nearer flight occurs adjacent a pole of theearth, the more rod 84 will tend to swing parallel to the plane of plateI.

The construction shown in Figure 8 provides means for using rod 84 as alimit stop for northward flight and southward flight. In the first caserod 84 will strike stop I56 which can be retracted through a slot inplate I, and in the second case the rod will strike stop [0! which canalso be retracted when desired. For southward flight rod 35 will act asa stop for sliding element 86 and. face 81a of cam 81, and for northwardflight the opposite side of rod 35 acts as a stop for the opposite faceof cam 81. A notched arm Bla, shown in fragmentary manner can be used'toalign arm or rod 84 in the same manner as previously described for arm8|. It is possible locked together.

Figure ishows a suspension for arm :84 supporting plumb bob 85; Fixedsupport I9 may be an extension of arm I9 shown in Figure 2 and bolt orscrew IDS is threaded into a hole in the end of arm I9, a suitablewasher being provided. Arm 84 can therefore swing through angles of 90or more across slot 95, .on either side.

Another suspensionis shown in Figure 3. .Rod 84 is attached to ball I09which is rotatable in any direction in spherical bearing or socket II9having a cut-out I I I across it to allow 90 move- 'ment of the rod ineither direction perpendicular the plane of the paper, and limitedmovement toward or away from post II2 having arm 3 -to which bearingsocket III i attached. Socket I IIl may be split, for assembly. Peakedro'd Bib is attached to the horizontal portion of arm 84 andisperpendicular to plate I, at the equator. Weight or plumb bob 85 isattached to rod 84 as before. Post H2 is fastened to plate I and weight85 has a bore through its right side face to receive solenoid coil II4.Non-magneticsleeve II5, carrying hook H6, i attached to coil H4 and hasa bore coaxial with the coil central opening. Cylindrical iron plungerII-I having an axial bore therein is slidable in the coil and sleeveopening and is normally pushed to the right against arcuate stop II8 bycompression spring II9 within the coil. Stop II8 consists of a strip ofmetal'or other material concentric with ball I89 and is spaced from andattached-to rod 35 fastened to ring 33 which is movable around gyroscopeshell 30, as previously described. Cylindrical plunger I ZB is made ofsteel and has a pointed right end adapted to engage a depression in stopH8, being urged in that direction by the compression spring shown in theaxial bore in cylindrical plunger III. The depression serves as a zeroor starting point of alignment for rod 84 and rod 35, arm 84b beingplaced near arm 35 for convenience. Hook I I6 serves asa means forpreventing spring I I-9 from pushing Weight 85 and arm 84b away from arm35. This hook is normally pulled against the right hand face of arcuatestrip I I8 by the springs.

It will be :seen that the rods are normally them for relativedisplacement, solenoid coil II4 is'suitably energized through flexibleleads I2I, and plunger II! is pulled into the solenoid at the same timethat pointed plunger I is magnetically pulled into plunger I29.Therefore strip I I8 .and rod are released so that there can be relativedisplacement of rods 84-8421 and 35 about their respective pivots, indirections perpendicular to the plane of the "paper. There is sufficientplay between hook H6 and strip IIS to allow limited free movement. Atthe end of the predetermined time interval of the test, the time clockI32 (Fig. 2) causes the solenoid circuit to be broken and plunger I20 isquickly forced against stop or holding strip H8 by spring II9 so thatthe rods 84b and 35 are locked in relative position by the frictionbetween plungers II] and I20 and strip H8. The adjacent surfaces can beroughened or otherwise treated to provide good frictional engagement.The spring urging pointed plunger I29 to the right is weaker than springH9 so that plunger I20 can, if desired, be forced back into its recesswhen plunger "I I1 and strip II8 are frictionally locked. Plunger I29 isforced to the right into 'the depression in strip IIB only when the twoare register, i. e., in starting position. The construction shown Whenit is desired .to release 12 makes it possible to align the two elementswith a pointed plunger and then to lock them together with largersurfaces.

The spherical shell 31 is constructed (as shown in Figure 2) and issupported by post 25 shown in fragmentary manner. A certain amount ofside play or cross movement of rods 84 and 35 is made possible by theball and socket construction and by the width of slot 39. This allowsfor normal fluctuations of the aircraft and for curvature of the flightpath at angles to the direction of flight; Like parts are given likedesignations as before, in :Figures 3, 4, and 5, and in other figures.

Ball I99 and gyroscope ring 33 carrying rod 35 are rotatable about anaxis passing through the center of the ball and ring and alignedparallel with the plane of plate I. Rods 84 and 35 can therefore beswung about :this axis even though they are locked together. This isnecessary in order to swing the two rods back to the positions shown inFigure l, for instance, for northward flight, ;since at any latitudeother than at the equator the two locked rods swing at an angle withrespect to Plate I and not perpendicularly as shown.

In order to swing the two rods, locked together after a 'periodofrelease, cross rod I22 (Fig. 2), attachedto arm I23, is provided. Thisarm is pivoted at I24 to post 20"and :is normally held up in the dottedposition-shown, by'tension spring I25 attached to the arm and to arm"I9, a suitable stop being provided. Bar I22 is therefore normally outof the way of rods 84 and 35 and weight or plumb bob '85. These rods mayswing leftward about their pivots in clockwise direction as seen inFigure 2. After they are finally locked together, however, fora groundspeed determination, arm I23 is-rotated counter clockwise about pivotI24 so that cross bar I22 strikes rod 84 and forces the tworods aroundto the position shown, with the lower end of .rod 84 striking slide 86as a stop. Another suitablestop could be arranged, however.

In order to cause this counterclockwise movement of arm 4'23, arc'uatesolenoid I 26, concentric with pivot 124, is attached to post 29.Arcuate iron plunger I21 is attached at one end to arm I23 and ismovable in the curved space in the solenoid which can be energized bycurrent through conductors I28 and I29 lea'dingto battery or othercurrent source I30, through spring :switch eI'SI :which is normallyopen. This switch .is mounted Ion a short post on plate I and ispositioned so that it is struck by arcuate strip 88 'soon after this'str ip begins moving through its circular path. 'Th'eswitch ismaintained closed until the actuating button 12 or 73 is released. Whenswitch I3I is closed, therefore,solenoid I26 is energized to pullplunger I2? into it and to cause bar I22'to'bring the rods .35 and toproper position as described.

Timing device 'I32iis shown as a key wound "spring-driven device "but itcan be asynchronous motor or any other suitable timing means. Thehousing I32 is attached to the under surface of plate "I and contains aclock-like sprin and escapement for governing the rate of rotation ofshaft 133 having attached winding key I34. Cam I--35 having cam rise I36is fixed to shaft I53 and rotateswith it. Pin I37 on cam is normallyheld by catch I38 pivoted to housing 132 so that the cam is normallylocked in position with the drivingspring wound. This spring urgesthe-cam torot'ate in the direction of the arrow so that,

after release, the cam rise I36 will strike button I39 on resilientswitch arm I46 to force this arm and its attached contact toward contactI4! both of which are mounted on an insulating block I42 attached tohousing I32. The switch I45I4I will therefore be closed until cam riseI36 rotates past button I39 so that the resiliency of arm I49 will thenquickly move the contact away from contact I4I to open the circuit whichincludes battery I36, conductors I43 and I44, solenoids II4, I46, I41;conductor I28, and switch I49 leading to the other terminal of thebattery.

Solenoid H4 is shown in detail in Figure 3 but any suitable type ofmagnet or solenoid can be used. This solenoid, when energized, releasesrod 35 from locked relationship with arm 64. Solenoid I46 is fastened tospherical ring 33 by threads or otherwise and has plunger I45 the innerend of which passes through a hole in ring 33 and engages innerspherical shell 36 to lock the ring and shell against relative movementwhen the solenoid is energized. The compression spring shown surroundingplunger I45 is fastened to the plunger and to solenoid I46 and normallyholds the plunger tip, which may be sharpened, away from shell 30 sothat rod 35 may be freely moved with rod 84. The plunger is made of softiron or the like and may have a non-magnetic tip.

The plunger of solenoid I41 is made similarly but having iron tipsection I49 and joined brass section I56 around which tension springII', attached to the plunger and to solenoid I41, is coiled and normallyforces the inner tip of plunger I49 against inner gyroscope shell I1 tolock it against movement relative to outer gyroscope shell I8. SolenoidI41 is suitably attached to shell I8 and a hole is provided in thisshell for passage of plunger I49. The energization of solenoid I41therefore causes plunger I49 to be pulled outward against the tension ofspring I5I to release shell I1 to allow free movement of this shell andattached rod I6, relativeto shell I6.

Solenoid I48 is fastened to block I52 attached to post 26 or integraltherewith. (See also'Figure 1.) The plunger of this solenoid isrectangular iron bar I53 which is slidable parallel With plate I, in arectangular slot in block I52, and carries right angle arm I54 to whichconical point I55 is attached. This point is adapted to mesh withsimilar shaped depression in rod I6 to align this rod. Similarly,rectangular spaced bar I51 is slidable parallel to bar I53, in arectangular slot in block I52 and carries right angle arm I58 havingattached conical point I59 adapted to engage similarly shaped depressionE69 in the opposite face ofrod I6. Therefore if arms I54 and I58 aremoved toward each other to fixed adjacent positions each time a test isfinished, points I55 and I59 will cause alignment of rod I6 in adirection along the Y axis and the arms I54 and I58, pressing rod I6between them, will align that rod along the X axis. Rod I6 willtherefore be automatically reset to the same starting position for eachtest. Sufiicient slippage between plunger I49 and shell H can be allowedto permit the resetting or solenoid I41 can be energized while arms I54and I58 are being moved toward each other.

The means for producing coordinated movement of bars I53 and I51includes-slotted rocker arm I6I pivoted at I62 to post I63 extendingfrom block I52. Pins I54 and I65, in bars I53 and I51, respectively,cooperate with the slots in arm I6I as shown and cause proportionaldisplacement of one barin one direction when the other bar is displacedin opposite direction. Block I 52 may be of brass or other non-magneticmaterial and bar I53 is of iron except for joined end portion I53a whichis of brass. The junction is shown by the dotted line at I66. Therefore,when solenoid I48 is energized, part of the bar beyond junction I66 ispulled into it by magnetic action and bar I51 is simultaneously moved bypin I65 in opposite direction. Compression spring I61 resting againstblock I52 and urging bar I51 and integral flange away from block I52,normally keeps arms I54 and I58 retracted, in the positions shown.

Solenoids II4, I46, and I41 are simultaneously energized by the closingof switch I4III4I by cam rise I36 and they are simultaneouslyde-energized when the switch is opened. Itis assumed that switch I49 isclosed before any test. One terminal of solenoid I48 is connected to abattery terminal through connected wires I68, I28, and switch I49. Theother terminal of this solenoid is connected to the other terminal ofbattery R36 through normally open switch I69 having a resilient contactarm adapted to be struck by sharp cam I16 attached to the inner face ofcam I35 near its edge. The resilient contact arm is connected to wireI43 and the switch is mounted on housing I32 being suitably insulated.The sharp cam I16 strikes the resilient arm of switch I63 and closes thecircuit to solenoid 1 46 momentarily before switch I46I4I is closed.This insures that the arms I54 and I58 will re-set rod I6 to startingposition just before each test.

Solenoids I1I is attached to the forward face of block I52 and isconnected to wires I28 and I29 so that it is energized simultaneouslywith solenoid I26. Plunger I12 comprises an outer brass section joinedto an inner iron section which may extend into a recess in block I52.This plunger is pulled to the left against a suitable stop when solenoidIN is energized. Tension spring I13 attached to the plunger and to theblock normally holds the plunger retracted so that it will not interferewith movements of rod 84 in the Vertical or near-Vertical positionrelative to plate I. When rod I22 is pulled down by solenoid I26 plungerI12 is simultaneously moved a definite distance to the left to serve asa stop. This construction is not essential but allows for vibration anderratic movements of the rods 84 and 35.

Figure 5 shows an alternative support for the plumb bob 85 and rod 84.In this case the plumb bob is supported on stub shaft I14 attached toinner shell 30. The outer spherically curved bearing shell 31a is cutaway at I15 so that shaft I14 will have free movement within limits.Suitable collars on shaft I14 prevent axial movement of the bored upperend of rod 84 but allow free swinging movement in a plane perpendicularto the plane of the paper. Bearing half-shell 31a is fastened to postI16 attached to plate I. Sim-.- ilar bearing half shell or socket 31b isattached to post I16a. fastened to plate I, and stub shaft |14aextending from shell 38 in line with shaft I14 supports arm 84a carryingweight 85a adapted to balance weight 85. Rods 35 and 36 and ring 33 areas previously described. This construction allows gyroscope rod 35 to beturned in either direction to follow arm 84 which may be rotatedineither direction, for northward or southward flight. The balancedconstruction allows the plumb bob to remain parallel with the gyroscoperod so that there is little side relative movement.

15 Magnet l ldmattached' to weight 85',m'ay be energized to lock'i-ronrod 35 to it.

In Figures 1 and 2, arm l'll integral with handle H8, is pivoted to anedge of ring 2 by means of bolt I19 passing through collar I82. Grip orhandle I89 is parallel with handle I18 and has a right angle portionfixed to ring 3. Pawl I8I is pivoted at I83 to grip I80 and has extendedportion I84 adapted to be struck by thin cam I85 attached to handle I18,when the handle i pulled toward grip I80 about pivot I19. This cam thenstrikes extension I84 and lifts pawl IBI away from the adjacent edge ofring 3, against tension of spring I88 attached to the pawl and elementI88. The edge of ring 3 is preferably serrated or roughened so that pawlIBI will normally look ring 2 against rotation to ring 3.

Arm I'll has perpendicular portion I81 adapted to'pressplates 44 and SIdown against their supporting springs when handle Il8 is pulled towardgrip I88. This depression of plates 99 and frees cylinder 45 andintegral element 46 for lateral movement by shaft l? which is shifted byarm 54 as a result of rotation of cam 51.

Level I88 is fastened to plate I and may be of any suitable type,including the bubble type which indicates horizontal position in anydirection.

If there is no slippage between cylinder #35 and plate 44, or betweenelement 48 and plate 5|, these plates and slide I2 will be moved untilstopped by a wedge I4 or I5 locking against rod I6, when a button '12 orI3 is pushed; spring BI being wound by movement of one of the racksafter stoppage of rotation of cylinder 45 and shaft 47. Therefore whenthe actuated button is released, its associated spring will move therack back to starting position and cylinder .45 and element 46 will berotated through the same angle to return plates is and 5I and slide I2to the starting'position. In order to allow for slight slippage, V block89 is attached to the rear end of slide I2 and vertical V slot I95 isout in the right face of slide 58'. Similarly shaped finger IHIisattached to bar I92 which carries another V finger I93 at lower leveland adapted to 'engage V groove I99. Finger I9I is adapted to engagegroove I89. Rectangular bar I92 is slidable parallel to plate 'I in arectangular slot inblock 194 fastened to plate I. tened to block 69 andto pin i95 attached to bar I92 normally holds fingers I-QI and I83pulled to the right against block :94. When, however, the end of arm 16is pulled around by spring 89 to strike cam I91 integral with bar I92,weaker spring I 95 is overcome and fingers I-9I and I93 are moved to theleftto engage respective grooves I89 and I99 to align slides I2 and 59accurately at their starting positions.

As shown in Figure 2 pendulum or weight I98 is suspended from attachedring 8 in a plane passing through the center of the ring andperpendicular to the plane thereof. This weight may be much larger thanindicated and serves to maintain ring 3 aligned about pivots 4 withrespect to the center of gravity of the earth. U-shaped magnet I99 isfixed to plate 6 and provides a magnetic field through weight I98 sothat eddy currents induced into this metal will cause damping to preventexcessive oscillation. Any other type of damping device such as a bathof viscous liquid around weight I98 can be used. The parts supported byplate I are so distributed that this plate is balanced about pivots 4.Extra balancing weights can be attached to plate I for Tension spring I95 fasthat purpose, if necessary. Therefore hanging weight I98 can swingin an east-west direction since the axis .passing through pivots 4 iskept pointing true north during a test. Plate '6, carrying posts 5, canbe rotated around pivot 8 to maintain the Y axis passing through pivots'4 pointing true north. Base plate I is ordinarily fixed to the aircraftand is parallel with the floor, or horizontaL This plate can beadjustable though or the aircraft can be manipulated tokeep the plane ofplate I horizontal or tangent to the earth, during any test. Level 200attached to plate 6 can be observed to show when the plates. arehorizontal.

It will be seen that, during the period of a speed.determinationslastingfrom say 1 minute-to. 10 minutes, as desired, the plate I will be.rotated in an east-west direction relative to gyroscopically controlledrod I6 and so the east-west ground speed component, if any, will beindicated. Unless provision is made to keep the plane of plate I exactlyparallel with the axis of the earth there will be a certain amount ofturning of plate I due to travel in a north-south direction at constantaltitude but this component of rotation of the plate, being small, will'havea negligible efiect upon theapparent movement of rod I6 ineast-West direction. Compensation for this'could be provided however.The northsouth turning of plate I causes plumb bob .85 and attached armor rod 84 to swing relative to gyroscopically controlled rod 35 so thatthe north-south ground speed component is indicated, the axis ofgyroscope 22 being parallel with the axis of theearth to avoidprecession.

If desired a gimba-l mounting for ring 3 can be provided so that itcanbe moved in any direction or it can be mounted to be rotatable in itsown plane relative to pivots i. This refinement is hardly necessary forusual purposes however.

Figure 9 illustrates how plate I is aligned parallel with the axis ofthe earth regardless of latitude. This illustration also shows modifiedsupports for ring 3. These supports 28! are thin arcuate bearingsfitting into a circumferential groove around the edge of ring 3. Thisring is therefore supported and guided by elements 29I and can berotated relative to them. Ring 3 could therefore be rotated to holdplate I parallel with the earths axis, during a test. This illustrationshows the alignment of plate -I for any test but bearings 20! are notessential.

In Figure 10 trapezoidal wedges or cams I4 and I5 are fastened torespective cross slides I41) and I52) slidable at right angles to thelong axis of slide I2 in keyways I and I cut in slide I2 and havingflared edges to prevent the slides from slipping out. Bars Md and I5dare screwed to the floors of the keyways and serve as stops for leftwardmovement of slides I 41) and I5b. Thumbscrew I ie is threaded through avertical hole in slide Mb and may be screwed down against the keywayfloor to lock the slide in either of its two positions. Similarlythumbscrew I56 serves to lock slide [5b in either of its two positions.V

Fragmentary Figure 19 shows the initial relative positions of wedges I4and I5 and gyroscope rod I8 for north-by-east and north-by-west flight,assuming that arrow NS parallel with the Y axis is directed to the truenorth. The trailing lower edge IBa of rod I6 overlaps edge Ma of wedgeI4 by a distance equal to that travelled by edge Ma relative togyroscopically controlled'rod I6, due to the 'earths rotation,during'the predetermined test interval of free relative movement;

Therefore, considering that the aircraft is stationary relative to theearth, the edge I60. of rod I6 will apparently move to the right untilit is in register with edge I4a during the aforesaid interval asdetermined by the timing device to be described later. In this relativeposition wedge I4 is locked against movement along the Y axis toward rodI6 but any further relative displacement beyond edge I 4a as a result ofdue-east speed of the aircraft will allow the wedge and slide I2 to bemoved toward rod I6 along track I3 until a point or line on face I4)strikes edge Ito and is stopped thereby. The faster the dueeastcomponent of ground speed of the aircraft the further will edge I iaapparently move to the right of edge I 411 and the greater the distancewedge I4 willbe moved along the Y axis until stopped by rod I6.Therefore the displacement of wedge I4 in a direction toward rod I6along track I3 is a measure of the due-east component of ground speed ofthe aircraft.

Edge I5) of generally opposed wedge I5 is placed to the right of leadingedge I 61) of rod I6 a distance equal to that travelled toward edge I6bat the end of rod I6 by edge I51 due to the rotation of the earth,during the automatically timed interval of the test, considering thatthe aircraft carrying the instrument is stationary with respect to theearth. Apparently, rod I6 moves to the right during this interval untiledge I612 is in register with edge I5f of wedge I 5 and so this wedge isblocked from movement toward rod I6 along track I3. If, however, theaircraft flies north-by-west, or due west, the circular displacement ofthe aircraft westward will cancel a portion of the circular displacementin space of the aircraft eastward, due to rotation of the earth, and soedge I6b will not reach edge I5f by a distance corresponding to thedue-west component of ground speed of the aircraft. Wedge I5 can then bemoved with slide I2 toward rod I6 until stopped by edge I61) and theamount of this movement is a measure of the due west component of speedof the aircraft relative to ground. It is assumed that the speed offlight is less than the circumferential rotational speed of the earth.If the aircraft speed is greater the wedges can be specially set.

. It is assumed in the above description that the aircraft flies atsubstantially constant altitude and speed during the test. Since theheight of the aircraft above the ground is small compared to the radiusof the earth, considerable variation of altitude of flight may bepermissible without seriously affecting the results. Suddenaccelerations should be avoided during tests. Arcuate scale 640 (Fig. 3)concentric with ball I09, will indicate the vertical position of arm 84,suitable indices being provided. The instrument can include means forshifting or changing scales or any other means for compensating forflight at different. altitudes, if desired. The plate I, or plate 6 canbe properly aligned by gyroscopic means if desired.

In the above-described speed determinations slide I4b is locked by screwI46, against stop bar I40! and slide I5b is locked by screw I5e in theposition shown, with the right edge of the slide in contact with theedge of keyway I 50.

Now contrariwise, if the aircraft is flyinggenerally southward, and ifthe instrument remains fixed relative to the aircraft, rod I6 willappear to move to the left as shown in Figure 11 and the slides andattached wedges I4 and I5 have'to be shifted and locked in position,with the right 18 edge of slide Mb adjacent the edge of keyway I40 andwith the left edge of slide I5b adjacent the stop bar I5d. Rod I6 isshown in usual starting position and the above shifts of the wedgesbring edge [4g of wedge I4 to a point overlapping edge I60 of rod I6 bya distance equal to the timed apparent shift to the left of rod I6relative to the edge I49, due to rotation of the earth and accompanyingatmosphere, and assuming that the aircraft is stationary with respect tothe earth. If the aircraft is flying south byeast, then the apparentdisplacement of rod I6 to the left, due to the component speed of theaircraft due-east, will be added to the displacement due to the earth'srotationand wedge I4 can be movedv toward rod I6 until. its leftinclined face strikes edge I60 and is stopped thereby. The amount ofextra displacement parallel with the -X' axis of edge I60 relative toedge Hg is then proportional to the true east ground speed component ofthe southeastward-flying aircraft and accordingly this ground speedcomponent can be measured by the relative displacement of wedge I4 withre;- spect to its associated scale. Wedge I5, in Figure 11, is shown insuch position that its edge I5g is displaced to the left of edge "id. ofrod I6 adistance equal to thedistance apparently moved by edge id to theleft during the timed interval, due to rotation of the earth and itsatmosphere, the rod I6 being of course gyroscopically maintained in itsalignment in space. Therefore edges H311 and I59 will be brought intoregister during the timed interval, by rotation of the earth, and if theaircraft is flying southwestward then part. of the apparent due-eastdisplacement of edgeIIid toward edge I5g will be cancelled. The great:-er the due-west component of ground speed the further edge I6d will 'beto the right of. edge I So at the end of the timed interval and, thefurther wedge I5 can be moved parallel with track I3 toward rod I6before its right inclined edge strikes edge Mid and is stopped thereby.This displacement of wedge I5. and attached slide I2 is therefore ameasure of the due-west ground speed component of thesouthwestward-flying aircraft and can be read with respect to its as:

sociated scale. 4

The preceding discussion assumes that the edge lb of plate I is forwardfor both northward and southward flights and that arrow NS points truenorth in the first case and true south in the latter case. When theflight isnorthward plumb bob rod 84 swings toward edge Ia of plate Isince it points toward thecenter of gravity of the earth. When theflight is southwardarm 84 swings in opposite direction relative .to.slide 86 and cam 81 and these elements should be initially sufficientlyshifted sidewise so that they do not obstruct movement of rod 84, and-rod.3 5 to which it is locked. The gyroscope rod 3 dv can be suspendedas shown in Fig. 5 and rod 84 can be suspended as illustrated in Fig. 3or Fig. 4.

Cam 8! can have two inclined faces as shown in Fig. 8 or the rods 84 and35, afterbeing locked together again after their relative displacement,can be rotated to the same side of cam 81 as that shown in Fig. 1, therotation being effected by another cross rod similar to rod I22 butacting in opposite direction while shifting the rods 84 and 35 which canthen be pressed against the slide or another stop as indicated. Theshifting of cam 81 will occur after this procedure.

When the aircraft is travelling northward,

"plumb bob rod 84 will lag behind gyroscope rod 35 and thus will rotaterelatively clockwise about its pivot (Fig. 2) due to curvature of theearth, during the timed period in which it is free to move relative togyroscope rod 35 which remains fixed relative to plate I when ring 33 islocked to its supporting shell 30. When the aircraft is travellingsouthward plumb bob rod 84 will still tendto increase its lag behind rod35 even though bothrods in this case will be on the opposite side ofslide 86, since the aircraft is flying in reversed direction. The tworods can, after finally being locked together, be swung to the same sideof cam 81 as indicated in Figure 2. Rod 8 is shown in a lagging positionwith respect to rod 35, as it would be after temporary release from rod35- during the timed interval. When rod 84 is pressed against slide 86or any other suitable stop by V arm BI, rod 35 then actsas a stop tolimit movement of cam 87 to the left, pulled by cable 94a. attached topin 94 extending, from slide 86' and attached to the end of spring 93after passing around pulley 93a potatably fastened to. plate I by screw93b, as described.

Since cam 81 is narrowed from right to left it willibe seen that themore the relative displacement between rods '84 and 35 the further thelatter will project toward cam 8'! from the fixed or stop position ofrod 84 and therefore the less slide. 86 will be moved to the left whenpulled .by cable 94a and spring 93 which is pulled to the right by arm19 when one of the buttons 12- or .13 is pressed. Therefore, since scaleO-N increases from O to the right an increased displacement between rods84 and 35 will cause a proportionately increased indication of the northor south ground speed component on scale ON'.

In operation, suppose that the aircraft is flying southwestward in thenorthern hemisphere. Wedges I4 and I5 are arranged as shown in Fig. 11,.for southward flight and handle H8 is squeezed toward grip H30 and ring2' is rotated until index B is. in register with the latitude of flightas. indicated on scale Sw, the latitude being known. This arranges plateI parallel with the axis of. the earth, assuming that plate 6 ismaintained horizontal by observing level 200. Arrow EW is held pointingdue west for the interval of the test. Then. rod 84 is locked to rod 3.5by causing pin I20, for instance to fall into the aligning depression instrip I I8 and the two rods are allowed to swing around their pivots bygravity until their axes point to the center of gravity of the earth,being suitably damped by magnet 85a or any other damping means. Thencatch l38 is pressed to release pin I 3'! so that cam I315 is rotated inthe direction of the arrow at uniform speed, with the result that camI18 momentarily closes switch H59 to energize solenoid' I48 and so toalign rod I6 at starting position. Then as the cam continues to rotate,cam rise I36 closes switch l40I4-I which causes energization ofsolenoids H4, I46, and [41, resulting in release of rod 84 or weight 85from rod 35 and in locking ring 33 to gyroscope shell 30, as well as inunlocking gyroscope shell I! for free movement relative to outer bearingshell [3; These conditions continue until the rotating cam rise I3 6passes button I39 and causes switch I40-I'4I to break the circuit to thethree solenoids after the time interval as predetermined by the arcuatelength of cam rise I36, and its rotational speed. Then rods 84 and 35are locked again relatively, and simultaneously ring 33 is unlocked fromshell 30, and shell I! is again locked relative to shell I3.

During the timed interval, rod 84 and rod 35 will have shifted relativeto each other as previously described, so that rod 84, or 84b, if used,will trail rod 35 by an amount representing the true southward groundspeed component. Likewise, during the same timed interval rod I6 willhave been apparently rotated or shifted relative to wedge l5, due to thecombined rotation of the earth and the due-west component of groundspeed of the aircraft. Then marked key or button T2 is pushed towardblock 6-?! its full travel. This causes pin T4 to rotate arm I9 andarcuate cam 80 clockwise about pivot 18; closing switch I31 to energizesolenoids I26 and HI, resulting in arm I23 swinging rod [22 down toforce relatively locked rods 84 and 35 against slide 86 as a stop, arm M(or a if that construction is used) striking the stop. Shortly afterclosing switch I3l, cam 83 and arm 8! will align rod 84 in the positionshown in Figure 1 and spring 93 will, by means of cable or cord 94a,pull slide 86 to the left (Fig. 1) until cam 8-1 strikes projecting rod35 and is stopped thereby, leaving tube 99 and cross hairs I03 in theposition shown, indicating the due-south ground speed component.

During this time, cylinder 45 is rotated by rack 61 in a direction tomove slide I2 along track I3 toward edge Ib of plate I, until wedge I5strikes locked rod I 6 and is stopped by it. In the meantime rotatingelement 45 will have moved slide 50 in the same direction as slide I2but through less distance, in the same proportion that the circumferenceof the earth at the latitude of flight bears to the circumference of theearth at the equator. Therefore the duewest ground speed component isrepresented by the position of the axis of pivot I95 with respect toscale OW. The true resultant ground speed can then be read on scale Icein terms of the distance from the axis of pivot I95 to the intersectionof cross hairs I 03. The drift and direction of flight can be observedas explained previously. Then key 12 is released and the various springscause the associated parts to be re-set to zero or starting position aspreviously described. Key I34 is then turned to rewind the spring of thetiming device and to rotate cam pin I31 back to be locked by catch I33.A suitable ratchet allows rewinding of the spring.

If the flight had been made in northwestward direction, in the northernhemisphere, index B would be turned to be in register with the properlatitude indication on scale Se, in order to place plate I parallel withthe axis of the earth and arrow EW would be pointed due east. If theflight were innortheastward direction index 13 would be set also withrespect to scale Se and 'arrow- EW would be also maintained pointed dueeast. The settings of wedges l4 and I5 would however be changed fornorthward flight as indicated in Figure 10. It is assumed in the abovediscussion that arrow NS is maintained pointing due north for northwardflight and due south for southward flight.

A chart of the simple changes necessary for northward or southwardflight can be provided or indices can be arranged so that moving acontrol element will automatically make the changes or indications ofchanges needed.

Figure 14 illustrates an electrical ground speed indicator based uponthe earths magnetic field.

21' Casing 204 is of metal and may be of iron to serve as a shieldagainst magnetic fields as well as an electrostatic shield. Long tube205 is of copper or other suitable metal and is screwed into a threadedhole in a wall of the casing, as shown, flange 206a acting as a stop.Copper or other metal wire or rod 206 extends for nearly the full lengthof tube 205 and is supported coaxially therewith by passing throughcentral holes in mic/a, porcelain, or other insulating discs 20'! whichmay be cemented or forced on the rod 206. Threaded porcelain or otherinsulating bushing 208 is screwed into inner threads at the end of thetube. Bushing 208 has a .central hole through which rod 206 passes andis rigidly fastened thereto, with cement or otherwise. Electricalcontact 209, preferably of the same metal as rod 206, is integraltherewith or is fastened to the rod by threads or in any suitablemanner. It is preferable that element 209 be of the same metal as rod206 in order to avoid contact and thermoelectric potentials.

Contact 210 is attached to rod 211 which is attached to plate 212 bythreads or otherwise. The contact 210, rod 211, and plate 212 are allmade of the same metal as contact 209 and rod 206, in order to avoidcontact potentials and thermo-E. M. F.s. Plate 212 is mounted inpercelain insulators 213 screwed to a wall of the casing. Contact button214, made of the same metal as the other contacts, is screwed intoBakelite or other insulating disc 215 fastened to thin flexible metalarm 216 anchored in metal block 211 screwed to the casing wall.

Magnet 218, fastened to the right casing wall over a hole therein,causes flexible arm 216 to vibrate at a relatively rapid rate whenenergized with current from battery or other current source 219.Conductor 220 leads from terminal A of battery 219 and is connected withmakeand-break contact 221 adapted to close the circuit to magnet 218through arm 216 when in contact therewith. Arm 216 is connected with aterminal of the magnet the other terminal of which is connected by wire253 to contact arm 222 mounted on insulating block 223 fastened to thetop of box 224. Flexible contact arm 225, having cam portion 226, isalso fastened to insulating block 223 and is biased to keep the contactsseparated normally. Contact arm 225 is connected to terminal B of thebattery by wire 221. Therefore, the closing of contacts 222 and 225causes battery 219 to energize magnet 218. Shielding housing 228 may beplaced around magnet 218 and the make-and-break contact and may be madeof iron or other metal. It is preferably made of iron in order toconfineboth magnetic and electrostatic stray fields to the housing. Slot229 in the housing allows arm 216 passing therethrough to vibrate.

Metal plate 230 is fastened centrally to Bakelite or other insulatingrod 231 and is joined to iron rod 232 at 233, by means of threads orotherwise. Iron rod 232 extends to junction 234 at which anotherBakelite rod 235 is joined to the iron rod. This composite rod isslid-able in a centrally positioned space in solenoid 236 which issuitably fastened to Bakelite bushing 23'! at junction 238. Bushing 231has flange 239 and is threaded into a hole in the left Wall of casing204. The bushing and integral sleeve 240 have a central bow to guide rod231-232 in sliding movement. Com,- pression spring 241 surrounding rod231 and from contact 249 which it normally touches.

Contact 249 is supported by metal rod 250 fixed in insulator 251 whichis fastened in a hole in wall 245. Rod 250 is connected to one terminalof electrical instrument 252 attached to the cas ing, outside wall 245.The other terminal of the instrument is connected with plate 230 byflexible wire 253. Magnet 248 is connected with conductors 220, and 253leading from switch arm 222 and battery terminal A to terminals ofmagnet 218. Instrument 252 may be a ballistic galvanometer, amicroammeter, or voltmeter, or the like.

Terminal B of the battery is connected to contact arm 254 by wire 255.Arm 254 is mounted on insulating block 256 fastened to the top of box224. Flexible contact arm 263 having cam portion 264 is also mounted oninsulator 256 and is normally biased to move away from contact 256. Whenhowever cam rise 25'1 strikes portion 264 the contacts are closed sothat terminal B of the battery is connected to one terminal of solenoid236 through wires 255 and 265. The other terminal of the solenoid isconnected to battery terminal A by conductor 266. The energization ofsolenoid 236 causes iron rod 232 and attached plate 230 to be pulled tothe left until the plate finally strikes contact 261 connected to groundwhich may be the casing or the metal framework of the aircraft or both.

Casing 204 is provided with a suitable metal cover which is preferablyof iron. Cam 256 having cam rise 25'! is fastened to shaft 258 which isrotatable in suitable bearings in box 224 and is driven by a clock-likespring. The rate of rotation of the shaft is goverened by an associatedgear train and escapement, as in a clock, and a ratchet can be providedfor rewinding the shaft and cam to starting position by means of key259. The cam is normally held in the starting position shown, againsttorsion of the spring, by spring catch 260 pivoted to the box top andhaving catch 261 engaging notch 262 in the cam. The cam may be releasedfor spring-driven clockwise rotation at uniform rate by pulling catch261 out of the notch.

In operation, conductor 206 is fixed in or on the aircraft so that itslength is at right angles to the fore-and-aft axis of the aircraft. Itmay extend from one wing tip to the other or only part of that distance.Casing 204 is placed in any suitable location, at the end of conductor206 as shown and key 259 is turned to wind the spring of the timingdevice including cam 256. The winding is continued until catch 261engages notch 262. Then as the aircraft flies along, preferably in astraight line, catch 261 is pulled back to release cam 256 which is thenrotated clockwise at constant speed so that cam rise 25'! strikes camportion 226 and closes switch 222225. This causes battery 219 toenergize magnets 218 and 248 simultaneously so that switch arm 243 ismagnetically pulled away from contact 249 and arm 216 is startedvibrating. This arm is normally biased to touch contact 221. Thevibration of arm 216 causes metal button 214 to touch, first,

potential.

23 contact 209 and then contact2|0 alternately at a relatively rapidrate.

Rod 206, is so aligned that, as it is swept through the earths magneticfield by the flying aircraft, an electron pressure or E. M. F. forcingelectrons inv conductor 2% toward contact 239 is developed. Thereforeeach time that metal button 214 touches contact 269 it receivesadditional electrons from this contact and additional electronsaccordingly are transferred to contact 2") connected with plate 212 whenbutton 216 is swung over to touch contact 2H2. These transferredelectrons are then distributed over plate 212 and, due to its relativelylarge capacitance, it can store a considerable quantity of electronsbefore its potential or electron density is made so high, in thenegative sense, that it will not receive further electrons from button21 Button 215 need not be normally in contact with element Zillas themomentum of swing will bring it into contact even if normally slightlyseparated.

In order to supply additional electrons to conductor 296, resilientcontact 258 is mounted on insulator 26s and is electrically connectedwith conductor 2% by wire 21a Therefore after button 2 l 4 is moved awayfrom contact 269, grounded metal arm 21% touches flexible contact 288and conductor 2% is brought to ground potential again. Contact 268 isnot essential if conductor 206 is of sufficient volume to supply all theneeded electrons without developing excessive positive Button 214 cansimilarly be grounded after leaving contact 2 l 0, if desired.

Switch 243249 is maintained open while the vibrating button 2| 4 istransferring electrons,

which operation continues until the trailing end of cam rise 251 passescam portion and so switch 222225 opens again. When that happens magnets248 and 218 are deenergized so that the vibrator stops after the timedinterval, and switch 243249 is closed, with the result that the excesscharge of electrons on plate 212 passes through instrument 252 and intoplate 230 which can be grounded if desired but is shown as beinginsulated. The quantity of electrons accumulated in plate 212, asindicated by their flow through instrument 252, will be a measure of thespeed of the. aircraft relative to ground, since the timed interval isthe same for each test and the electron pressure toward contact 209 willvary in proportion to the speed of the conductor 296 relative to thevertical component of the earths magnetic field at the location of thespeed determination. Variations of the strength or direction of theearths field can be compensated for as described later.

Resistor 2% can be connected between instru-- ment 252 and plate 230 tomake the discharge aperiodic, if desired, or a rectifier can be includedin the circuit if instrument 252 is of direct cur-- rent type.

As the trailing end of cam rise 251 rotates past .ca-m element 22% theforward end of the cam rise strikes cam element 264 to cause closing ofswitch 26.3254. This results in energizing solenoid 236 so that iron rod232 and connected plate 230 are pulled to the left. This separation willresult in a decrease of capacitance of the condenser formed by plates212 and 239. The plate 238 can be insulated or grounded and, if

insulated it can be arranged to strike grounding metal strip 212 when itis near plate 2l2 so that induced positive. charges on plate 230. willbe held when the plate is separated from strip or contact 212.Therefore, as. plate. 230 is moved to the left thevoltage rises and canbe indicated by instrument 252'. When plate 236 finally touches element261 it is grounded again.

It is not essentialthat plate 23fl'be movable but it provides an addedeffect. The switches 222-425 and 254-253 can be located so that solenoid236 is energized after the closing of switch 243249, or before, orsimultaneously. Magnet 248 may be shielded, as well as other partslikely to produce stray fields or radiation.

Shielding tube 285 can be removed if desired, but is useful ineliminating or reducing static charges on conduct-or 2516. Plate 212 isgrounded after each discharge since connected plate 230 is grounded atleast at times. A suitable motor could rotate cam 256 to give rapidlyrepeated ground speed indications.

Figure 15 shows a modified electrical ground speed indicator. Like partsare givenlike reference characters as in Figure 14. In this caserotatable disc 2|6a driven by shielded motor 218a, sweeps contacts firstpast resilient contact 2090. and then past resilient contact 21011. Asbefore, these contacts, the contacts or buttons on disc 216a, and rod226 and plate 2I2 are made of the same metal. Disc 215a is made ofBakelite or other electrically insulating material and has imbeddedmetal buttons 214a extending from one face of the disc to the other at auniform radius from the center. These buttons are flush with the facesof the disc so that they will make smooth contact with elements 259a andHim as they pass. The left face of the disc has only the equally spacedmetal contact buttons showing through but the right face has also thinmetal strips 268a extending radially outward from connected motor shaft213 which is grounded, the motor ZlBa being fastened to metal casing284. The strips 268a are imbedded in the right face of the disc and areilush with the surface. They are situated midway between buttons 214aand extend nearly to the disc edge. Contact or brush 210a is placed sothat any button 214a will first brush past contact 259a to collectelectrons and then will come into contact with brush 210a to depositthem.

Contact 2 l 0a is supported on insulator 214 and is connected to switcharm 215, fastened to insulator 215. by wire 219. Contact arm or switcharm 211 having cam portion 218, is resilient and is normally separatedfrom contact arm 215. Contact arm 211 is connected to plate 2| 2 by wire235. Wires 218, 2813, contact arms 215 and211 and plate 2|2 are all madeof the same metal of which contacts 209a, 2llla and rod 206 are made.

Plate 236a is of the same metal as plate 2|2, preferably, and is mountedin insulating bars 213a fastened to the casing. Plate 238a is parallelto and adjacent plate 212, and metal plate 281 is also supported in bars213a, and adjacent plate 230a and parallel thereto as indicated. Thenegative terminal of battery or other relatively high potential'source262 is connected to plate 28l by wire 283 and the positive terminal ofthe battery is connected to resilient switch. arm 284by Wire 285. Switcharm 284 has a cam portion which is struck at times by cam rise 288 oncam 221a fastened to shaft 258 along with cam 255 but displaced axiallytherefrom. Switch contact arm 281 is normally separated from. contactarm 284 and is electrically connected with plate 23% by wire 283..Therefore when contacts 284 and 281 are momentarily touched together andseparated plate 239a is. left with a positive charge, i. e., a.deficiency of electrons.

i late 281 can be grounded at the same time that contacts 284-481 areclosed, if desired.

Plate 212 is connected to flexible cam switch arm 289 by wire 299.Associated switch arm 291 is normally separated from arm 289 and iselectrically connected with cathode 2920f electronic amplifying tube 293the grid 294 of which is connected to wire 288 and plate 239a by wire295. If desired, grid bias battery 298 may be connected as shown to biasthe grid negatively with respect to cathode 292. If bias battery 295 isused, resistor 291 of relatively high resistance should be connectedbetween wire 295 and wire 298 connecting cathode 292 to switch arm 291.This switch is made as described for the other switches and is alsoattached to the top of box Shielded motor 299 is attached to box 229 andhas pulley 399 in contact with the circularrim of cam 256. Cam rise 251is displaced axially so that it will not strike pulley or friction disc399. When the motor is energized by current from battery 219 it revolvescam disc 256 clockwise, and attached cam rise 251 which closes for aperiod switches 215211, and 299291 in the order named. Likewise cam rise285 momentarily closes switch 284-481.

Terminal A of current source 219 is connected to one terminal f m0t0r219a and to one terminal of motors 299 and 329. These motors should beof constant speedvtype and may be of synchronous design. Terminal B ofcurrent source 219 is connected to switch contact 391 which can beconnected when desired to conductor 392 connecting the other terminalsof motors 2180., 299 and 329,

by closing connected switch arm 393.

In this case also, a spring motor couldbe used to drive the cams but anelectric motor is shown so that continuous revolution of the cams can beachieved when desired. V I

The anode of tube 293 is connected to the positive terminal of batteryor other potential source 394 the negative terminal of which isconnected to a terminal of instrument 252. The other terminal of thiselectrical indicating instrument is connected to cathode 292 which issuitably energized.

Instrument 252 is mounted on plate 395 and has pointer 395 rotatableabout pivot 391. Arcuate scale 398 is concentric with pivot 391and iscalibrated, preferably, in miles-per-hour ground speed. Arcuate rod 309of silicon steel, soft iron, or the like is attached to the left end ofscale 398 concentric therewith. Similarly arcuate rod 319, of anysuitable metal, is attached to the other end of scale 398 concentrictherewith. Bearing posts 311 and 312 having holes therethrough extendupward from plate 395 and serve to guide rod 319 and attached scale 398in an arcuate path. Rod 399 is movable in arcuate solenoid 313 attachedto plate 395. Compression spring 314 surrounding rod 319 and pressingagainst bearing 3| 1 and collar 315 on rod 319, serves nor-' mally tourge rod 319 clockwise-untilcollar 316 on rod 319 strikes bearing 311 asa stop.

When solenoid 313 is energized arcuate plunger 399 is magneticallypulled into it against thetension of spring 314 for a distanceproportional to the'current passing through the solenoid winding.Therefore if current through solenoid 313 is proportional to theeffective magnetic field strength of the earth, i. e., thevertical-component, then scale 398 will be moved through an arcproportional to the earths effective field strength. The tension ofspring 314, the strength of solenoid 313, and the scale markings ofscale 398 can then be so correlated, and with respect to pointer 396that scale 398 will be properly shifted relative to the pointer tocompensate for variations of, the earths effective field strength. Suchvariations will include changes of magnetic. field strength as well asdirection. Limited compensation is therefore provided.

In, order to vary the current in solenoid 313 in proportion to theeffective earths field, a generator is provided the output of whichvaries with the effective component of the earths field. Rectangularwindings 311 and 318, consisting of many turns of fine wire, areattached to shaft 319 of motor 329 on opposite sides of the shaft, bymeans of bands 321 or inany other manner. The shaft may have two opposedflat surfaces. Slip ring 322 is attached to shaft 319 and has anassociated brush connected with cathode 328 of electronic amplifyingtube 324. Commutator 325 comprises an insulating disc of Bakelite or thelike attached concentrically to shaft 319 and carrying small contactplugs 329 and 321 diametrically opposite and imbedded in the disc sothat their outer surfaces are concentrically .curved and are flush withthe edge Of the disc.

One terminal of winding 311 is connected to slip ring 322 and the otherterminal is connected to contact 321 by a conductor passing through anaxial bore in the shaft. Similarly, one terminal of winding 318 is alsoconnected to slip ring 922 and the other terminal of thiswinding inconnected to contact 326. Suitably supported brush 329 makes contactwith plugs 326 and 321, alternately, as shaft 319 is revolved by motor329. Brush 329 is connected with grid 323 through bias battery 339 whichcan be arranged to bias the grid either negatively or positivelybutnegative biasingis shown. 7

Winding 311 is fixed to shaft 319 so that the outer leg is at the apexof its circular travel, as indicated, when plug 321 is in contact withbrush 321. The coil is phased so that the, electromotive force generatedby the coil linking the earths, magnetic field is applied to cathode 328and grid 323 with such polarity that grid 323 is made positive or lessnegative with respect to the cathode. The result is that current passingthrough the, tube, and solenoid 313 connected in series therewith isincreased. The anode of tube 324 is con.- nected to the positiveterminal of battery or other. potential source 331 the negative terminalof which is connected to cathode 328, with solenoid 313 in series.

Since the E. M. F. generated by rotating winding 311 is effective in thecircuit only when in the topmost position shown, when the outer leg istravelling horizontally for a moment, the effective momentary E. M. F.controlling tube 324 is proportional to the vertical component of themagnetic field of the earth at that location. This is still trueregardless of the direction of'travel or magnetic field strength ordirection, for all determinations sa'y north of the equator. Theconnections from the brushes to the grid and cathode'respectively, canbe reversed for determinations south of-the equator. Even close to theequator there is still a vertical magnetic field component.

As winding 31'! is rotated past its vertical position indicated, plug321 leaves brush 329 and breaks the' grid circuit until plug 326 isrotated to a position in contact with brush 329. Winding 319 will thenoccupy the position shown by winding 311 and is phased to supply thegrid circuit.

with another positive pulse proportional to the vertical component ofthe earths magnetic field. Grid leak 332 can be connected-between thegrid and cathode if desired.

If motor 326 revolves shaft 3|9 fast enough the rapidlyrecurring-positive pulses will be almost continuous in efiect, but astorage condenser can be used if desired. It will be seen therefore thatthe output current through tube 324 and solenoid 3|3 will be inproportion to the vertical component of the earthsmagnetic field. Scale308 and the associated parts are calibrated, as previously described, sothat the scale will be shifted to compensate for variations of theefiective vertical component of the earths field. If, for instance,pointer 333 is in the same position for a weaker field as for a strongerfield it indicates that the aircraft is travelling faster in the weakerfield and scale 338- will be shifted clockwise to bring a higher scalereading into register with the pointer. The device can be calibrated fora weak field or a strong field and the output of the rotating windingscan be applied totube 324 to reduce the current therethrough instead ofincreasing it. as. described. In that case scale 308 would be movedclockwise to compensate for stronger fields and itwould be calibratedaccordingly, in conjunction with pointer 306. While the compensatingeffect isshown asbeing accomplished by a scale shift, the output of tube324 can be applied to the electrical circuits of instrument 252 toefiect compensation without moving the scale. One method ofaccomplishing this is to connect an electronic tube between battery 304and instrument 252 and then to apply potentials from the anode circuitof tube 324'to the grid circuit of the added tube, in order to changethe resistance of the circuit including the instrument. Therefore,considering a constant speed of the aircraft, if the-earths fieldbecomes weaker than the calibrating field, so thatinstrument 252 mightshow a lower speed than the actual value, the resistanceof theadded tubewillbe correspondingly lowered-so that more current will flowthroughinstrument 252 and it will indicate correct ground speed. It can becalibrated to show correct speeds for wide changesof eifective fieldstrength. Switch 339 is provided to cut solenoid 3 [3- out of circuitwhen desired.

Another construction for compensating for variations of the efiectivecomponent of the earths field includes solenoid 340. and associat edcomponents. This solenoid is connected to.

ried by plunger 3,43 andv is. electrically connected. This contact is.movable along resistor 34'! connected to cathode.

with spring '344 and wire 34,5.

292. Therefore when plunger 343 is energized contact 346. is moved alongresistor 34'! so that the resistance in the instrument circuit isincreased and the. current therethrough is, correspondingly reduced. Thevalue. of the resistor,

and the strengths of solenoid 340 andspring 344.

canbe so chosen that the. device will compensate for. variations offield strength. If, for instance,

the aircraft flies through a weaker field than the calibratedvvalueythe: energizing. pulses; through.

tact 346 in a direction to reduce the resistance and so to increase thecurrent through instrument 252 and vice versa. The inertia of thesolenoid plunger will cause it to hold a fairly steady position eventhough the energization of the solenoid is fluctuating. It is notessential to use solenoid M3 in this case and it can be cut out of thecircuit by switch 339.

The various motors and switches described in the foregoing pages arepreferably shielded to eliminate interference from stray fields. Theconductors likewise should be shielded. Wherever thermoelectric efiectsor contact potentials might interfere, as for instance in conductors238' and 296, these should be made of the same metal as all connectedcomponents.

In operating, conductor 2% extends across the aircraft as previouslydescribed. Shaft M 9 is aligned parallel with conductor 235. Now if theaircraft is flying in the northern hemisphere, say, then the gridconnections of tube 32d are as shown and switch 353 is closed to startconnected motors 2l3a, 299, and 320 revolving. Assuming that the motorsare revolving at their constant speeds, as plugs Z-Ma rub againstcontact 2990. due to rotation of disc 2 Isa in clockwise direction asviewed from the right, each plug will collect electrons from contact209a due to the electron density developed in that contact'as a resultof the E. M. F. generated in conductor 266 as it is swept through thevertical component of the earths magnetic field. At least part of theelectrons removed from contact 209a will be transferred to contact' 2i0aas disc Zita carries the. plugs further around the circumference totouch contact Zita. Theel'ectrons are not-transferred. to plate 212however until switch 2'i521.l' is closed' by rotating cam rise 25 1.

Before'swit'ch 2 15-21-1- is closed; however, cam rise 286 closes switch284-28Ifor a moment. to leave plate 230w positively charged.Thispositively charged plate, being adjacent. plate..2 l2.,

4 the extreme right endlof thisrodcan. be. grounded solenoid 340 willvbe weaker and spring 344 will accordingly: pull plunger- 343. andattached; C0117.

permanently by connectingit to:the. metal frame-- worle or toshield205;. This;construction. .supplies. adequate electrons. to. rod; 2 3 6'but reduces its. iso

lation.

Switch 2154-2111 is thenclosed by. rotating; cam rise 251 andis-amaintainedi closedi for the same time .intervab each time ithat camrise 2 5:1; ispassing beneath cam= element 218.. While the switch isclosed, therefore, the: individual extra electron-charges oniplugs21.42:..are. imansferred toxplate 2 [2 through.- conductors. 2-19 and280- and switch 2-15-4332. As cam: 25.& continues. to rotate clock--wisercami ri'sez 253-? closes. switch. 239.=-2 3 I: so thatelectronfiowi from-i plate2 12". to positively chargedplate: 230::passes; through resistor 2.9.7. and biases grid 294: positively. The.resulting increase of current; through: instrument 252: causes pointer306' to indicate thelspeediofr the. aircraft relative to ground-.; The.tube,:233:may normally be biased to cuteoff, or; for. a. predetermined.current which willcause; pointer 3.06 to, register azero reading.Therefore as:the:cams =revolv.e and;the aircraft flies;v its; course.repeatedindications: of ground speed: areishown; byi pointer, 305.relative toscale.

